adding epub fails

[BryanW]

Calibre is having trouble adding some (but not all) of my epubs. I tried re-installing program, no luck. The problematic epub files appear functional as they will add to ibooks and are readable without any issue. Adding problematic epub files from ibook directory also results in same error.

System- MacBook Pro with OS 10.12.6 Beta

calibre, version 3.6.0
WARNING: Errors while adding: There were problems adding some files, click "Show details" for more information

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Failed to add the file /Users/Bryan/Desktop/Misc/Books/Neal Stephenson/Sevenenes - Neal Stephenson.epub to the book: /Users/Bryan/Desktop/Misc/Books/Neal Stephenson/Sevenenes
With error:
Traceback (most recent call last):
  File "site-packages/calibre/gui2/add.py", line 430, in add_formats
  File "site-packages/calibre/db/cache.py", line 1406, in add_format
  File "site-packages/calibre/startup.py", line 122, in local_open
IOError: [Errno 21] Is a directory: u'/Users/Bryan/Desktop/Misc/Books/Neal Stephenson/Sevenenes - Neal Stephenson.epub'

[Kovid Goyal (kovid)]

Those are not epub files. They are directories whose names end with
.epub. A bit of googling will find you scripts to convert these
directories created by ibooks into actual epub files.

 status invalid